Mitral pressure half-time: is it a valid measure of orifice area in artificial heart valves?

The Hatle orifice area formula was derived in patients with significant mitral stenosis and was not intended for use in other situations. Comparisons between it and other methods of estimating orifice area have shown variability in the slope of the regression lines with wide dispersal of data points. There is no relationship in prosthetic valves between pressure half-time and annulus diameter. Pressure half-time is determined by a number of factors other than orifice area, notably left ventricular compliance, the square root of the peak transmitral pressure drop at the start of diastole, and stroke volume. In normal prosthetic valves, therefore, pressure half-time reflects non-prosthetic factors more accurately than orifice area, and other formulae, such as the continuity equation, should be used to assess the latter. A pressure half-time prolonged beyond 200 ms remains a useful indication of obstruction, especially when the peak transmitral velocity is high.